Epinephrine on the NCLEX
Epinephrine for anaphylaxis (IM thigh) and cardiac arrest (1 mg IV): routes, timing, auto-injector teaching.
One drug, two emergencies, two very different doses. The NCLEX loves to see whether you know which is which.
Anaphylaxis: IM, thigh, first
Epinephrine IM into the vastus lateralis (outer thigh) is the first drug in anaphylaxis. Adult dose 0.3-0.5 mg of the 1 mg/mL concentration, repeatable every 5-15 minutes. Antihistamines and steroids are adjuncts. Any answer that gives diphenhydramine before epinephrine in true anaphylaxis is wrong.
Why IM beats subcut and IV here
The thigh muscle absorbs fast and reliably even when perfusion is dropping. Subcutaneous absorption is too slow in shock. IV bolus epinephrine in a patient with a pulse risks lethal arrhythmias, so IV epi in anaphylaxis is reserved for refractory cases as a dilute infusion with monitoring.
Cardiac arrest: a different dose
ACLS uses 1 mg IV/IO every 3-5 minutes during cardiac arrest, any rhythm. This is the higher-dilution IV preparation, pushed during CPR and followed by a flush. Keep the two contexts separate: arrest gets 1 mg IV; anaphylaxis with a pulse gets 0.3-0.5 mg IM.
Auto-injector teaching
Inject through clothing into the outer thigh, hold in place per device instructions, then call 911 even if symptoms improve: reactions rebound. Carry two devices; up to a third of reactions need a second dose. Check expiration dates and replace cloudy or discolored solution. Massage the site briefly after injection.
After the epi
Position supine with legs raised unless breathing is easier upright. Oxygen, IV fluids for hypotension, and observation for biphasic reactions, which can return hours after the first symptoms resolve.
Frequently asked
Patient with hives and wheeze after a bee sting. First drug?
Epinephrine IM in the thigh. Not diphenhydramine, not albuterol first.
Why call 911 after using an auto-injector that worked?
Biphasic reactions recur hours later, and one dose may not be enough. The device buys time; it does not end the emergency.
What side effects should the patient expect?
Pounding heart, tremor, pallor, anxiety. Brief and expected. They are not a reason to withhold a needed dose.
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